WP8.1 Listpicker throws (Error HRESULT E_Fail has been returned from a call to a COM component)

Question

1. Windows Phone Databound project targeting WP 8.1 OS.
2. Added WPToolkit through NuGet

3. Added toolkit reference to the page:

   xmlns:toolkit="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls.Toolkit"

4. Added a list picker and gave it items source.

When I deploy to the phone it is working just fine. But in the designer I get this error, and it's pretty annoying, I was wondering if I can do something about it?

UPDATE:

Restarting visual studio solved the problem.